Water heating system and a method of operating same

ABSTRACT

A hot water system ( 10 ) comprising a water storage tank ( 14 ) and an instantaneous-type water heater ( 12 ). The water storage tank ( 14 ) has an inlet ( 22 ) and outlet ( 24 ). The instantaneous-type water heater ( 12 ) has an inlet ( 18 ), in fluid communication with a mains water supply ( 26 ), and an outlet ( 20 ), in fluid communication with the inlet ( 22 ) of the tank ( 14 ). The water heater ( 12 ) energises in response to a flow of water through the water heater ( 12 ).

FIELD OF THE INVENTION

The present invention relates to a water heating system and a method of operating same.

The present invention has been primarily developed for use with gas instantaneous type water heaters and will be described hereinafter with reference to that application. However, the invention is not limited in this particular field of use and can also be used with electrical instantaneous-type heaters. In the United States of America, instantaneous-type water heaters are known as tank-less heaters.

BACKGROUND OF THE INVENTION

Known instantaneous type heaters have an inlet, connected to a mains water supply, and an outlet connected to, for example, a tap. The flow of water through the heater automatically energises the gas burners or electrical elements therein. This known arrangement has two disadvantages.

The first disadvantage relates to water wastage. When a user activates a hot water tap, the user must wait for the mains supplied water to be heated, and for all the unheated water in the pipes between the heater outlet and the tap to be purged, before receiving the heated water at the tap. The Australian Federal Government departments concerned with water conservation estimate that usage of this type in an average household occurs about 19 times a day and wastes up to 90 litres of water a day.

The second disadvantage relates to two types of gas wastage. The first type of gas wastage occurs because, as mentioned above, known instantaneous type heaters ignite their burners upon sensing flow of water through the heater, caused by opening a hot water tap. In the case of a shower, the heater takes some time to come up to temperature and the cool-to-warm water delivered in the intervening heating period is often dumped to waste by the householder. The second type of gas wastage occurs because many users only turn on the hot tap when washing their hands, wash in the initial cold-to-lukewarm water, and then simply turn off the tap. In that situation, gas is used to solely go through a start up phase and heated water is left in the pipes, which then cools and is thus wasted.

It is an object of the present invention to reduce water and gas wastage in water heating systems utilizing an instantaneous-type water heater.

SUMMARY OF THE INVENTION

Accordingly, in a first aspect, the present invention provides a hot water system comprising:

a water storage tank having an inlet and outlet; and

an instantaneous-type-water heater having an inlet, in fluid communication with a mains water supply, and an outlet, in fluid communication with the inlet of the tank,

wherein the water heater energises in response to a flow of water through the water heater.

The tank is preferably insulated.

The tank outlet is preferably in fluid communication with a user controlled valve, such as a tap.

In a second aspect, the present invention provides method of operating a hot water system, the method comprising:

supplying mains water to an inlet of an instantaneous-type water heater;

energising the instantaneous-type water heater in response to the water being supplied thereto;

directing the heated water from an outlet of the instantaneous-type water heater to an inlet of a water storage tank; and

directing the heated water from an outlet of the tank to a user controlled outlet.

In a third aspect, the present invention provides a hot water system comprising:

a water storage tank having an inlet and outlet;

an instantaneous-type water heater having an inlet, in fluid communication with a mains water supply, and an outlet, in fluid communication with the inlet of the tank; and

a controller adapted to: receive a signal indicative of the temperature of the water in the tank; and issue a control signal to the water heater,

wherein the controller is adapted to energise the water heater in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or below a first predetermined value.

The controller is preferably also adapted to not energise, or de-energise, the water heater in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or above a second predetermined value.

The controller is preferably also adapted to not energise, or de-energise, the water heater in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or above the first predetermined value and substantially equal to or below the second predetermined value.

The controller is preferably also adapted to issue control signals to the water heater which vary the amount of energy applied to the water therein and thus the temperature of the water leaving the water heater.

The first predetermined temperature value is preferably about 55 Degrees C. The second predetermined temperature value is preferably about 75 Degrees C.

In one form, the hot water system includes a first temperature sensor at or near the middle of the tank.

In another form, the hot water system includes a first temperature sensor at or near the top of the tank and a second temperature sensor at or near the bottom of the tank and the controller is adapted to energise the water heater in response to the second temperature sensor indicating a temperature substantially equal to or below the first predetermined value. The controller is preferably also adapted to not energise, or de-energise, the water heater in response to the first temperature sensor indicating a temperature substantially equal to or above the second predetermined value. The controller is preferably also adapted to not energise, or de-energise, the water heater in response to the second temperature sensor indicating a temperature substantially equal to or above the first predetermined value and the first temperature sensor indicating a temperature substantially equal to or below the second predetermined value.

The controller is preferably also adapted to issue control signals to the water heater which vary the amount of energy applied to the water therein and thus the temperature of the water leaving the water heater.

In a fourth aspect, the present invention provides a method of operating a hot water system, the method comprising:

supplying mains water to an inlet of an instantaneous-type water heater;

directing the water from an outlet of the instantaneous-type water heater to an inlet of a water storage tank;

directing the water from an outlet of the tank to a user controlled outlet;

monitoring the temperature of the water in the tank; and

energising the instantaneous-type water heater in response heater in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or below a first predetermined value.

The method preferably includes not energising, or de-energising, the water heater in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or above a second predetermined value.

The method preferably includes not energising, or de-energising, the water heater in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or above the first predetermined value and substantially equal to or below the second predetermined value.

The first predetermined temperature value is preferably about 55 Degrees C. The second predetermined temperature value is preferably about 75 Degrees C.

The method preferably also comprises varying the amount of energy applied to the water by the instantaneous-type water heater to vary the temperature of the water leaving the water heater.

In a fifth aspect, the present invention provides a hot water system comprising:

a water storage tank having an inlet and outlet;

an instantaneous-type water heater having an inlet, in fluid communication with a mains water supply, and an outlet, in fluid communication with the inlet of the tank, the water heater being adapted to energise in response to a flow of water through the water heater; and

a diverter valve having:

an inlet in fluid communication with the mains water supply; a first outlet in fluid communication with the inlet of the water heater; and a second outlet in fluid communication with the inlet of the tank; and

a controller adapted to: receive signals indicative of the temperature of the water in the tank; and issue control signals to the valve,

wherein, when the valve is actuated, the controller is adapted to control the diverter valve to direct water to the first outlet in response in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or below a predetermined value, and to direct water to the second outlet in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or above the predetermined value.

The first predetermined temperature value is preferably about 55 Degrees C. The second predetermined temperature value is preferably about 75 Degrees C.

In one form, the hot water system includes a first temperature sensor at or near the top of the tank and a second temperature at or neat the bottom of the tank and, when the valve is actuated, the controller is adapted to control the diverter valve to direct water to the first outlet in response in response to the second temperature sensor indicating a temperature substantially equal to or below a predetermined value, and to direct water to the second outlet in response to the first temperature sensor indicating a temperature substantially equal to or above the predetermined value.

The controller is preferably also adapted to issue control signals to the water heater which vary the amount of energy applied to the water therein and thus the temperature of the water leaving the water heater.

In a sixth aspect, the present invention provides a method of operating a hot water system, the method comprising:

supplying mains water to an inlet of an instantaneous-type water heater or an inlet of a water storage tank;

directing the water from an outlet of the tank to a user controlled outlet;

monitoring the temperature of the water in the tank; and

directing the mains water to the inlet of the instantaneous-type water heater in response in response to the temperature of the water in the tank being substantially equal to or below a predetermined value, and directing the mains water to the inlet of the water storage tank in response to the temperature of the water in the tank being substantially equal to or above the predetermined value.

In a seventh aspect, the present invention provides a hot water system comprising:

a water storage tank having an inlet and outlet; and

an instantaneous-type water heater having an inlet, in fluid communication with a mains water supply, and an outlet, in fluid communication with the inlet of the tank, the water heater being adapted to energise in response to a flow of water through the water heater; and

a first pump having an inlet, in fluid communication with an additional outlet of the tank, and an outlet, in fluid communication with the inlet of the water heater; and

a controller adapted, upon user instruction, to energise the pump and cause water to direct water from the outlet of the water heater to the inlet of the tank and from the second outlet of the tank to the inlet of the water heater, in order to heat the water in the tank.

Preferably, the controller is adapted to vary the speed of the pump, so as to vary the dwell time of the water passing through the heater and thus the temperature of the water at the outlet of the heater.

The additional outlet of the tank is preferably at or near the top of the tank and the second inlet of the tank is preferably at or near the bottom of the tank.

In a variation of this embodiment, the additional outlet of the tank is at near the top of the tank and the tank inlet is at or near the middle of the tank.

In an eight aspect, the present invention provides a method of operating a hot water system, the method comprising:

energising a pump to direct water from into the inlet of an instantaneous-type water heater;

energising the instantaneous-type water heater in response to water flow therethrough;

directing the heated water from the outlet of the instantaneous-type water heater to the inlet of a water storage tank; and

directing the water from an outlet of the tank to the inlet of the instantaneous-type water heater,

whereby the water in the tank can, upon user instruction, be circulated through the instantaneous-type water heater to heat the water in the tank.

The method preferably also comprises varying the speed of the pump, so as to vary the dwell time of the water passing through the heater and thus the temperature of the heated water at the outlet of the heater.

In a ninth aspect, the present invention provides a hot water system comprising:

a water storage tank having first and second inlets and first, second and third outlets;

an instantaneous-type water heater having an inlet, in fluid communication with the first outlet of the tank, and an outlet, the water heater being adapted to energise in response to a flow of water through the water heater;

a first pump having an inlet, in fluid communication with the outlet of the water heater, and an outlet, in fluid communication with the first inlet of the tank;

a second pump having an inlet, in fluid communication with the mains water supply and the second outlet of the tank, and an outlet;

at least one solar panel having an inlet, in fluid communication with the outlet of the second pump, and an inlet, in fluid communication the second inlet of the tank; and

a controller selectively adapted to energise the first and/or the second pump and cause water to circulate between the water heater and the tank and/or between the at least one solar panel and the tank respectively.

The first outlet of the tank is preferably at or near the top of the tank. The second outlet of the tank is preferably at or near the bottom of the tank. The third outlet of the tank is preferably at or near the top of the tank. The first inlet of the tank is preferably at or near the middle of the tank. The second inlet of the tank is preferably at or near the middle of the tank.

In a tenth aspect, the present invention provides a method of operating a hot water system, the method comprising:

energising a first pump to direct water from into the inlet of an instantaneous-type water heater;

energising the instantaneous-type water heater in response to water flow therethrough;

directing the heated water from the outlet of the instantaneous-type water heater to the inlet of a water storage tank;

directing the water from an outlet of the tank to the inlet of the instantaneous-type water heater;

energising a second pump to direct water into the inlet of at least one solar panel;

directing the heated water from an outlet of the at least one solar panel to an inlet of a water storage tank; and

directing the water from an outlet of the tank to the inlet of the at least one solar panel,

whereby the water in the tank can be circulated through the instantaneous-type water heater and/or the at least one solar panel to heat the water in the tank when required.

In an eleventh aspect, the present invention provides a hot water system comprising:

a water storage tank having first and second inlets and first and second outlets;

an instantaneous-type water heater having an inlet and an outlet, in fluid communication with the first inlet of the tank, the water heater being adapted to energise in response to a flow of water through the water heater;

a pump having an inlet, in fluid communication with the first outlet of the tank and with a mains water supply, and an outlet;

a diverter valve having: an inlet in fluid communication with the outlet of the pump; a first outlet in fluid communication with the inlet of the water heater; and a second outlet;

at least one solar panel having an inlet, in fluid communication with the second outlet of the diverter valve, and an outlet, in fluid communication the second inlet of the tank; and

a controller adapted to selectively energise the second pump and to control the diverter valve to direct water to the first outlet to circulate water between the water heater and the tank or to direct water to the second outlet to circulate water between the at least one solar panel and the tank.

The diverter valve preferably includes a third outlet in fluid communication with atmosphere.

The first outlet of the tank is preferably at or near the top of the tank. The second outlet of the tank is preferably at or near the bottom of the tank. The first inlet of the tank is preferably at or near the top of the tank. The second inlet of the tank is preferably at or near the middle of the tank.

In a twelfth aspect, the present invention provides a method of operating a hot water system, the method comprising:

energising a pump;

directing water from an outlet of the pump into:

-   -   (1) an inlet of an instantaneous-type water heater;     -   energising the instantaneous-type water heater in response to a         flow of water through the heater;     -   directing the heated water from the outlet of the         instantaneous-type water heater to the inlet of a water storage         tank; and/or     -   (2) directing the water from the outlet of the pump to an inlet         at least one solar panel;     -   directing the heated water from an outlet of the at least one         solar panel to an inlet of a water storage tank; and     -   directing the water from an outlet of the tank to the inlet of         the at least one solar panel,

whereby the water in the tank can be circulated through the instantaneous-type water heater and/or the at least one solar panel to heat the water in the tank when required.

The systems according to the second to twelfth aspects preferably include at least one water tank temperature sensor in signal communication with the controller. In one form, the system includes a first water tank temperature sensor near the top of the tank and a second water tank temperature sensor near the bottom of the tank. In another form, the system also includes a third water tank temperature sensor near the middle of the tank. The controller is preferably adapted to determine a temperature gradient across the height of the tank using at least two, more preferably three, of the first, second and third temperature sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of a first embodiment of a water heating system;

FIG. 2 a is a schematic view of a first version of a second embodiment of a water heating system;

FIG. 2 b is a schematic view of a second version of the second embodiment of a water heating system;

FIG. 3 is a schematic view of a third embodiment of a water heating system;

FIG. 4 is a schematic view of a fourth embodiment of a water heating system;

FIG. 5 is a schematic view of a fifth embodiment of a water heating system;

FIG. 6 is a schematic view of a sixth embodiment of a water heating system; and

FIG. 7 is a schematic view of a seventh embodiment of a water heating system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a first embodiment of a water heating system 10 comprising a gas instantaneous-type water heater 12, preferably of 4, 5 or 6-Star rating. The burners in the heater 12 are automatically energised upon sensing flow of water through the heater 12. The system 10 also includes a (buffer) water storage tank 14, preferably 4-50 litres in volume. The tank 14 is encased in insulation 16. The heater 12 has an inlet 18 and an outlet 20. The tank 14 has an inlet 22 and an outlet 24. The inlet 18 of the heater 12 is connected to a mains water supply pipe 26. The outlet of the heater 12 is connected to the inlet 22 of the tank 14 by a pipe 28. The outlet 24 of the tank 14 is connected to a user-controlled outlet device, such as a hot tap (not shown), by a pipe 30.

When the tap is initially actuated by a user, water flows from the mains supply pipe 26 into the heater 12 and is heated by the gas burners therein. The heated water then flows through pipe 28 into the tank 14 and, after the tank 14 is filled, through the pipe 30 to the user. Thereafter, when the user actuates the hot water supply, it can be drawn from the volume of heated water residing in the tank 14. This advantageously means that, whilst the water in the tank 14 remains sufficiently heated, the user does not have to wait for cold water to be heated and then supplied to them. The system 10 thus provides heated water to the user more quickly than the existing system described previously, thereby reducing the amount of water that is otherwise wasted whilst the user waits for heated water to reach the tap. The system 10 also avoids wasting of the gas used that would have been used whilst the user is waiting. This effect can be optimized by positioning the tank (or multiple tanks) near the user-controlled outlets (or outlets). Whilst the tank 14 does not require the insulation 16, the insulation 16 improves the retention of the energy supplied to the heated water in the tank 14. It should also be noted that the flow rate of the water leaving the tank 14 is limited by the capacity of the heater 12 to pass water under mains pressure.

A first version 40 a of a second embodiment of water heating system is shown in FIG. 2 a. The water heating system 40 a is similar to the water heating system 10 shown in FIG. 1 and like features have been indicated with like reference numerals. However, the water heating system 40 a also includes a controller 42. The controller 42 receives signals indicative of water temperature in the (4-50 litre) tank 14 from a sensor 44 which is positioned near the middle of the tank 14. The controller 42 is also connected to the heater 12 and is able to control whether or not the heater 12 is energised in response to water flow. As the heater 12 does not energise automatically in response to water flow, it can be simplified and is thus less expensive.

If the sensor 44 indicates to the controller 42 a water temperature of about 55 Degrees C. or less, then the controller 42 will energise the heater 12. If the sensor 44 indicates to the controller 42 a water temperature between about 55 Degrees C. and about 75 Degrees C., then the controller 42 will not energise the heater 12 or, if operating, de-energise the heater 12.

A second version 40 b of the second embodiment of water heating system is shown in FIG. 2 b, which is better suited for tank volumes of 50-400 litres. The water heating system 40 b is similar to the water heating system 40 a shown in FIG. 2 and like features have been indicated with like reference numerals. However, in the water heating system 40 b, the controller receives signals indicative of water temperature in the tank 14 from first and second sensors 44 a and 44 b, which are positioned near the top and bottom of the tank 14 respectively.

If the second/bottom sensor 44 b indicates to the controller 42 a water temperature of about 55 Degrees C. or less, then the controller 42 will energise the heater 12. If the first/top sensor 44 a indicates to the controller 42 a water temperature of about 75 Degrees C. or more, then the controller 42 will not energise the heater 12 or, if operating, de-energise the heater 12. If the second/bottom sensor 44 b indicates to the controller 42 a water temperature of about 55 Degrees C. or more and the first/top sensor 44 a indicates to the controller 42 a water temperature of about 75 Degrees C. or less, then the controller 42 will not energise the heater 12 or, if operating, de-energise the heater 12. The dual sensors 44 a and 44 b increase the sensitivity and accuracy of the control of the water heater 40 b.

The systems 40 a and 40 b reduce water wastage in the same manner as was described with reference to the water heating system 10. The systems 40 a and 40 b also reduces gas wastage as gas is not supplied to the heater 12 during the conditions described above, which could otherwise be wasted as previously described.

FIG. 3 shows a third embodiment of a water heating system 50. The water heating system 50 is similar to the water heating systems 40 a and 40 b shown in FIG. 2 a and FIG. 2 b and like features have been indicated with like reference numerals. However, in the water heating system 50, the controller 42 is also connected to a pump 52. The tank 14 also includes an additional outlet 54 which is connected to an inlet 56 of the pump 52 by a pipe 58. An outlet 60 of the pump 52 is connected to the mains water supply pipe 26 by a pipe 62.

If the second/bottom sensor 44 b indicates to the controller 42 a water temperature of about 55 Degrees C. or less, then the controller 42 will energise the heater 12. If the first/top sensor 44 a indicates to the controller 42 a water temperature of about 75 Degrees C. or more, then the controller 42 will not energise the heater 12 or, if operating, de-energise the heater 12. If the second/bottom sensor 44 b indicates to the controller 42 a water temperature of about 55 Degrees C. or more and the first/top sensor 44 a indicates to the controller 42 a water temperature of about 75 Degrees C. or less, then the controller 42 will not energise the heater 12 or, if operating, de-energise the heater 12. In addition, the controller 42 can, in response to a user instruction, energise the heater 12 and the pump 52 and cause water to circulate between the tank 14 and the heater 12 in order to pre-heat the volume of the tank 14. This is a particularly desirable feature for tanks 14 having relatively large storage volumes, such as 50-400 litres.

In this embodiment, the controller 42 determines if the water in the tank 14 has cooled, either due to usage or due to heat loss, and advantageously reacts accordingly. This embodiment also allows the entire volume of the tank 14 to be pre-heated on demand (for example, to stabilize water temperature in the tank 14) and then supplied at mains supply flow rates (for example, to fill a bath). This is advantageous in many situations as mains supply flow rates are higher than those of instantaneous-type heaters.

The speed of the pump 52 is dependant on the desired outlet temperature of the heater 12. The desired heater outlet temperature is dependent on the design of the heater 12 and incoming water temperature. For example, and generally speaking, for a given outlet temperature of say 70 Degrees C. and incoming mains water supply of 10 Degrees, the pump speed is set relatively slow to increase the dwell time of the water and maximize the efficiency of the heat transfer rates in the heater 12. However, if the incoming mains water temperature was 30 Degrees C., the speed of the pump 52 would be increased to maximize heat transfer in the heater 12. Ambient air temperature will also affect pump speed, but to a lesser degree.

The controller 42 can also vary the speed of the pump 52 in order to vary and control the dwell time of the water passing through the heater 12 and thus its resultant temperature. In addition, controlling the speed of the pump 52 can be used to influence the amount of mixing (stratification) and temperature degradation of the water in the tank 14. For example, generally speaking, a very high flow rate, such as 12 litres per minute, will cause the heated water entering the tank 14 to mix with the water already in the tank 14. However, a relatively slow flow rate, such as 5 litres per minute, results in the heated water not substantially mixing with the water already in the tank 14 and instead forming stratifications or layers within the tank 14. In these layers, the hottest water in the tank 14 is advantageously nearest to the outlet 24, and thus the user.

Controlling the water temperature by simply controlling the pump speed allows the cost of the water heating system 50 to be reduced as the relatively expensive control electronics required to, for example, regulate water heating by varying gas flow, flame intensity and/or flame size are no longer required. The heater 12 can instead be run at a constant (high efficiency) heat level and merely be switched on or off.

A fourth embodiment of a water heating system 70 is shown in FIG. 4. The water heating system 70 is similar to the water heating systems 40 a and 40 b shown in FIG. 2 a and FIG. 2 b except the controller 42 is connected to a diverter valve 72. The valve 72 includes an inlet 72 a connected to the mains water supply pipe 26, a first outlet 72 b, connected to the inlet 18 of the water heater 12 by pipe 74, and a second outlet 72 c, connected to the pipe 28 and thus to the inlet 22 of the pump 14 by a pipe 76. The controller 42 can control the valve 72 to direct water from the mains supply pipe 26 from the inlet 72 a to either the first outlet 72 b or to the second outlet 72 c. In this embodiment, the heater 12 automatically energises upon sensing a flow of water therethrough.

If the second/bottom sensor 44 b indicates to the controller 42 a water temperature of 55 Degrees C. or less, then the controller 42 will control the valve 72 to divert water from the main supply 76 to the first outlet 72 b and so to the inlet 18 of the water heater 12. As stated above, the heater 12 automatically energises upon sensing a flow of water therethrough caused by, for example, a user opening a hot water tap.

If the second/bottom sensor 44 b indicates to the controller 42 a water temperature of 55 Degrees C. or more and the first/top sensor 44 a indicates to the controller 42 a water temperature of about 75 Degrees C. or less, then the controller 42 controls the valve 72 to direct water from the mains supply 26 to the second outlet 72 c and thereby directly to the inlet 22 of the tank 14.

As with the heater 40, when the controller 42 senses that the water in the tank 14 is sufficiently heated, it controls the valve 72 to direct water from the mains supply 26 to the second outlet 72 c and thereby to the inlet 22 of the tank 14. As a result, these water volumes do not pass through the water heater 12 which is therefore not energised and gas usage is reduced.

Water usage is also reduced in the same manner as was described in relation to the water heating systems 40 a and 40 b.

In addition to the gas and water savings previously described, the water heater 70 also has the additional advantage that a very simple and inexpensive heater 12 can be utilized, without control components, as it simply automatically energises and operates at full capacity upon sensing a flow of water therethrough.

A fifth embodiment of a water heating system 80 is shown in FIG. 5. The water heating system 80 has components in common with the water heating system shown in earlier embodiments and like features have again been indicated with like reference numerals. The water heating system 80 has a gas (instantaneous-type) water heating circuit, indicated generally by the reference numeral 82, and a solar water heating circuit, indicated generally by the reference numeral 84. The gas circuit 82 includes a pump 84 having an inlet 86, connected to the outlet 20 of the water heater 12 by pipe 88, and an outlet 90, connected to an inlet 92 at about the middle of the tank 14. The tank 14 also includes an additional outlet 94 connected to the inlet 18 of the heater 12 by pipe 96. The solar circuit 84 includes a solar panel 98 and a pump 100. The outlet 102 of the pump 100 is connected to an inlet 104 of the solar panel 98 by a pipe 106. The solar panel 98 also has an outlet 108 connected to an additional inlet 110 of the tank 14 by pipe 112. The pump 100 also has an inlet 114 connected to an outlet 116 by pipe 118. The mains water supply pipe 26 is Tee'd into the pipe 118. The system 80 also includes a third temperature sensor 44 c near the middle of the tank 14 and a fourth temperature sensor 44 d at the outlet of the solar panel 98. Both of the sensors 44 c and 44 d are connected to the controller 42.

When the controller energises the first pump 84, water is circulated between the upper portion of the tank 14 and the water heater 12 in order to pre-heat same. When the controller 42 energises the second pump 100, and sufficient solar energy is available, water is circulated between the bottom portion of the tank 14 and the solar panel 98 in order to pre-heat same.

Generally speaking, the controller 42 determines when one or both of the pumps 84 and 100 are activated in order to best suit different expected demands. The controller 42 will always to attempt to heat the water using solar energy over gas energy. More particularly, if the temperature at the sensor 44 d is more than about 4 Degrees C. than the temperature at the sensor 44 c, then the controller 42 will energise the second pump 100 (of the solar circuit 84). The controller 42 will keep the second pump 102 energised unless there is less than about a 4 Degree C. difference between the sensor 44 d and the sensor 44 b or if the sensor 44 a indicates a water temperature of 80 Degrees C. or more. A temperature of 80 Degrees C. is acceptable in the lower part of the tank 14 as the heat will redistribute into the upper half of the tank if hot water is not being used.

If the third/middle sensor 44 c indicates to the controller 42 a water temperature of 55 Degrees C. or less, then the controller 42 will energise the pump 90 (of the gas circuit 82). The controller 42 will de-energise the pump 90 if the first/top sensor 44 a indicates a water temperature of about 75 Degrees C. or more. If the third/middle sensor 44 c indicates to the controller 42 a water temperature of 55 Degrees C. or more and the first/top sensor 44 a indicates a water temperature of about 75 Degrees C. or less, then the controller will not energise, or de-energise, the pump 90.

If the sensor 44 a indicates a water temperature of about 80 Degrees C. or more, then both the first pump 90 and the second pump 102 are de-energised, to prevent over-heating.

In addition, the controller 42 can, in response to a user instruction, energise the heater 12 and the pump 90 and cause water to circulate between the tank 14 and the heater 12 in order to pre-heat or stabilize the volume of the tank 14. This is a particularly desirable feature for tanks 14 having relatively large storage volumes, such as 50-400 litres.

A sixth embodiment of a water heating system 120 is shown in FIG. 6. The water heating system 120 is similar to the water heating system 80 shown in FIG. 5 and like components are indicated with like reference numerals. However, the water heating system 120 includes only a single pump 122 and a diverter valve 124 which has an inlet 126, a first outlet 128 and a second outlet 130.

When the controller 42 determines that water should be circulated through the gas circuit 82, the pump 122 is energized and the diverter valve 124 is controlled to divert water from the inlet 126 to the first outlet 128 and so to the inlet 18 of the water heater 12 by pipe 132. The heated water leaves the outlet 20 of the heater 12 and is supplied to an inlet 134 of the tank 14 by pipe 136. Water is drawn from an outlet 138 of the tank through pipe 140 into an inlet 142 of the pump 122. The pump also has an outlet 144 connected to the inlet 126 of the diverter valve 124 by pipe 146.

When the controller 42 determines that water should be circulated through the solar circuit 84, the pump 122 is energized and the diverter valve 124 is controlled to divert water from the inlet 126 to the second outlet 130. The second outlet 130 is connected to the inlet 104 of the solar panel 98 by pipe 148. The outlet 108 of the solar panel 98 is connected to an inlet 150 of the tank 14 by pipe 152.

The controller 42 will always to attempt to heat the water using solar energy over gas energy. More particularly, if the temperature at the sensor 44 d is more than about 4 Degrees C. than the temperature at the sensor 44 c, then the controller 42 will divert water through the solar circuit 84. The controller 42 will keep water flowing through the solar circuit 84 unless there is less that about a 4 Degree C. difference between the sensor 44 d and the sensor 44 b or if the sensor 44 a indicates a water temperature of 85 Degrees C. or more. A temperature of 85 Degrees C. is acceptable in the lower part of the tank 14 as the heat will redistribute into the upper half of the tank if hot water is not being used.

If the third/middle sensor 44 c indicates to the controller 42 a water temperature of 55 Degrees C or less, then the controller 42 will divert water through the gas circuit. The controller 42 will de-energise the pump 122 if the first/top sensor 44 a indicates a water temperature of about 75 Degrees C. or more. If the third/middle sensor 44 c indicates to the controller 42 a water temperature of 55 Degrees C. or more and the first/top sensor 44 a indicates a water temperature of about 75 Degrees C. or less, then the controller will divert water through the solar circuit 84.

In addition, the controller 42 can, in response to a user instruction, energise the heater 12 and the pump 122 and cause water to circulate between the tank 14 and the heater 12 in order to pre-heat or stabilize the volume of the tank 14. This is a particularly desirable feature for tanks 14 having relatively large storage volumes, such as 50-400 litres. It can also be desirable, because of regulations, to sterilise the tank 14 from time to time (e.g. for legionella control). For some authorities, this can be performed using the gas circuit 82 until the top and middle sensors 44 a and 44 c indicate 60 degrees C. or more. Alternatively, for other authorities, this can be performed using the gas circuit 82 until the top and bottom sensors 44 a and 44 b (ie. the whole of the tank 14) indicate 60 degrees C.

FIG. 7 shows a seventh embodiment of a water heating system 160. The system 160 is similar to the system 120 shown in FIG. 6 and like components have been indicated with like reference numerals. However, in the system 160, the diverter valve 124 also has a third outlet 162 which is connected to a pipe 164 which can drain to atmosphere, or for collection for re-use. If the controller 42 determines that the ambient temperature is cold enough to freeze water in the solar panel 98 and damage same, then the diverter valve 124 is controlled to direct water from the inlet 126 to the third outlet 162. This causes the water in the solar panel 98 to empty through pipe 164. Draining can also be performed to prevent over-heating of the solar panel 98. These draining operations are described in the Applicant's International PCT Patent Application No. PCT/AU2008/001476 filed 3 Oct. 2008, the relevant contents of which are incorporated herein by cross reference.

Although the invention has been described with reference to specific examples, it will be appreciated by a person skilled in the art that the invention can be embodied in many other forms. For example, the gas instantaneous water heaters can be replaced with electric instantaneous water heaters which results in electrical energy being saved instead of gas being saved. 

1-21. (canceled)
 22. A hot water system comprising: a water storage tank having an inlet and outlet; and an instantaneous-type water heater having an inlet, in fluid communication with a mains water supply, and an outlet, in fluid communication with the inlet of the tank, the water heater being adapted to energise in response to a flow of water through the water heater; and a diverter valve having: an inlet in fluid communication with the mains water supply; a first outlet in fluid communication with the inlet of the water heater; and a second outlet in fluid communication with the inlet of the tank; and a controller adapted to: receive signals indicative of the temperature of the water in the tank; and issue control signals to the valve, wherein, when the valve is actuated, the controller is adapted to control the diverter valve to direct water to the first outlet in response in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or below a predetermined value, and to direct water to the second outlet in response to the temperature signal indicating that the temperature of the water in the tank is substantially equal to or above the predetermined value.
 23. The hot water system as claimed in claim 22, wherein the first predetermined temperature value is about 55 Degrees C.
 24. The hot water system as claimed in claim 22, wherein the second predetermined temperature value is preferably about 75 Degrees C.
 25. The hot water system as claimed in claim 22, wherein the hot water system includes a first temperature sensor at or near the top of the tank and a second temperature at or neat the bottom of the tank and, when the valve is actuated, the controller is adapted to control the diverter valve to direct water to the first outlet in response in response to the second temperature sensor indicating a temperature substantially equal to or below a predetermined value, and to direct water to the second outlet in response to the first temperature sensor indicating a temperature substantially equal to or above the predetermined value.
 26. The hot water system as claimed in claim 25, wherein the controller is also adapted to issue control signals to the water heater which vary the amount of energy applied to the water therein and thus the temperature of the water leaving the water heater.
 27. A method of operating a hot water system, the method comprising: supplying mains water to an inlet of an instantaneous-type water heater or an inlet of a water storage tank; directing the water from an outlet of the tank to a user controlled outlet; monitoring the temperature of the water in the tank; and directing the mains water to the inlet of the instantaneous-type water heater in response in response to the temperature of the water in the tank being substantially equal to or below a predetermined value, and directing the mains water to the inlet of the water storage tank in response to the temperature of the water in the tank being substantially equal to or above the predetermined value.
 28. A hot water system comprising: a water storage tank having an inlet and outlet; an instantaneous-type water heater having an inlet, in fluid communication with a mains water supply, and an outlet, in fluid communication with the inlet of the tank, the water heater being adapted to energise in response to a flow of water through the water heater; and a first pump having an inlet, in fluid communication with an additional outlet of the tank, and an outlet, in fluid communication with the inlet of the water heater; and a controller adapted, upon user instruction, to energise the pump and cause water to direct water from the outlet of the water heater to the inlet of the tank and from the second outlet of the tank to the inlet of the water heater, in order to heat the water in the tank.
 29. The hot water system as claimed in claim 28, wherein the controller is adapted to vary the speed of the pump, so as to vary the dwell time of the water passing through the heater and thus the temperature of the water at the outlet of the heater.
 30. The hot water system as claimed in claim 28, wherein the additional outlet of the tank is at or near the top of the tank and the second inlet of the tank is at or near the bottom of the tank.
 31. The hot water system as claimed in claim 28, wherein the additional outlet of the tank is at near the top of the tank and the tank inlet is at or near the middle of the tank.
 32. A method of operating a hot water system, the method comprising: energising a pump to direct water from into the inlet of an instantaneous-type water heater; energising the instantaneous-type water heater in response to water flow therethrough; directing the heated water from the outlet of the instantaneous-type water heater to the inlet of a water storage tank; and directing the water from an outlet of the tank to the inlet of the instantaneous-type water heater, whereby the water in the tank can, upon user instruction, be circulated through the instantaneous-type water heater to heat the water in the tank.
 33. The method as claimed in claim 32, wherein the method also comprises varying the speed of the pump, so as to vary the dwell time of the water passing through the heater and thus the temperature of the heated water at the outlet of the heater.
 34. A hot water system comprising: a water storage tank having first and second inlets and first, second and third outlets; an instantaneous-type water heater having an inlet, in fluid communication with the first outlet of the tank, and an outlet, the water heater being adapted to energise in response to a flow of water through the water heater; a first pump having an inlet, in fluid communication with the outlet of the water heater, and an outlet, in fluid communication with the first inlet of the tank; a second pump having an inlet, in fluid communication with the mains water supply and the second outlet of the tank, and an outlet; at least one solar panel having an inlet, in fluid communication with the outlet of the second pump, and an inlet, in fluid communication the second inlet of the tank; and a controller selectively adapted to energise the first and/or the second pump and cause water to circulate between the water heater and the tank and/or between the at least one solar panel and the tank respectively.
 35. The hot water system as claimed in claim 34, wherein the first outlet of the tank is at or near the top of the tank.
 36. The hot water system as claimed in claim 34, wherein the second outlet of the tank is at or near the bottom of the tank.
 37. The hot water system as claimed in claim 34, wherein the third outlet of the tank is at or near the top of the tank.
 38. The hot water system as claimed in claim 34, wherein the first inlet of the tank is at or near the middle of the tank.
 39. The hot water system as claimed in claim 34, wherein the second inlet of the tank is at or near the middle of the tank.
 40. A method of operating a hot water system, the method comprising: energising a first pump to direct water from into the inlet of an instantaneous-type water heater; energising the instantaneous-type water heater in response to water flow therethrough; directing the heated water from the outlet of the instantaneous-type water heater to the inlet of a water storage tank; directing the water from an outlet of the tank to the inlet of the instantaneous-type water heater; energising a second pump to direct water into the inlet of at least one solar panel; directing the heated water from an outlet of the at least one solar panel to an inlet of a water storage tank; directing the water from an outlet of the tank to the inlet of the at least one solar panel, whereby the water in the tank can be circulated through the instantaneous-type water heater and/or the at least one solar panel to heat the water in the tank when required.
 41. A hot water system comprising: a water storage tank having first and second inlets and first and second outlets; an instantaneous-type water heater having an inlet and an outlet, in fluid communication with the first inlet of the tank, the water heater being adapted to energise in response to a flow of water through the water heater; a pump having an inlet, in fluid communication with the first outlet of the tank and with a mains water supply, and an outlet; a diverter valve having: an inlet in fluid communication with the outlet of the pump; a first outlet in fluid communication with the inlet of the water heater; and a second outlet; at least one solar panel having an inlet, in fluid communication with the second outlet of the diverter valve, and an outlet, in fluid communication the second inlet of the tank; and a controller adapted to selectively energise the second pump and to control the diverter valve to direct water to the first outlet to circulate water between the water heater and the tank or to direct water to the second outlet to circulate water between the at least one solar panel and the tank.
 42. The hot water system as claimed in claim 41, wherein the diverter valve includes a third outlet in fluid communication with atmosphere.
 43. The hot water system as claimed in claim 41, wherein the first outlet of the tank is at or near the top of the tank.
 44. The hot water system as claimed in claim 41, wherein the second outlet of the tank is at or near the bottom of the tank.
 45. The hot water system as claimed in claim 41, wherein the first inlet of the tank is at or near the top of the tank.
 46. The hot water system as claimed in claim 41, wherein the second inlet of the tank is at or near the middle of the tank.
 47. A method of operating a hot water system, the method comprising: energising a pump; directing water from an outlet of the pump into: (1) an inlet of an instantaneous-type water heater; energising the instantaneous-type water heater in response to a flow of water through the heater; directing the heated water from the outlet of the instantaneous-type water heater to the inlet of a water storage tank; and/or (2) directing the water from the outlet of the pump to an inlet at least one solar panel; directing the heated water from an outlet of the at least one solar panel to an inlet of a water storage tank; and directing the water from an outlet of the tank to the inlet of the at least one solar panel, whereby the water in the tank can be circulated through the instantaneous-type water heater and/or the at least one solar panel to heat the water in the tank when required.
 48. The hot water system as claimed in claim 5, wherein the system includes at least one water tank temperature sensor in signal communication with the controller.
 49. The hot water system as claimed in claim 48, wherein the system includes a first water tank temperature sensor near the top of the tank and a second water tank temperature sensor near the bottom of the tank.
 50. The hot water system as claimed in claim 49, wherein the system also includes a third water tank temperature sensor near the middle of the tank.
 51. The hot water system as claimed in claim 49, wherein the controller is adapted to determine a temperature gradient across the height of the tank using at least two of the first, second and third temperature sensors.
 52. The hot water system as claimed in claim 49, wherein the controller is adapted to determine a temperature gradient across the height of the tank using all of the first, second and third temperature sensors. 